Highly alloyed stainless steels and nickel-base alloys are finding wide usage as tubular products in deep, high-pressure, sour gas well applications. The environments in each application will vary but the range of conditions where alloy tubulars are utilized in the oil and gas industry may contain pressures between 15,000-20,000 psi and temperatures up to 450.degree. F. with H.sub.2 S contents ranging between 50 ppm to 40%. Most deep gas wells will contain water with high salt contents which further increase the agressiveness of the environment.
A high degree of corrosion resistance is required for alloys in deep, sour gas applications. As the temperatures, pressures, and H.sub.2 S contents, and possibly CO.sub.2 contents, in gas well environments increase, the severity of corrosion increases. Carbon and low alloy steels can no longer be utilized successfully because of their high corrosion rates. Corrosion inhibitors may not provide adequate protection in these wells. In some cases, the environment temperatures exceed the effective inhibitor temperature range. In other wells, the dynamic flow conditions do not permit proper maintenance of the inhibitor films. Finally, corrosion inhibitor utilization requires, in many cases, the construction of additional off shore platform space and continuing manpower requirements, making alloy tubular goods a more economical choice for combating corrosion.
In these highly aggressive environments, the tubular alloys need to possess high strength. The increased strength is required, both (1) to contain the higher pressures encountered in the service and (2) to support the weight of the longer string of tubing. In order to achieve these strength levels, alloy tubulars are usually cold worked, for example, by pilgering, cold drawing, or other suitable methods. Although each application will have its particular specification, the mechanical properties required for tubulars in deep gas wells may range from a yield strength of 110,000 psi to 180,000 psi.